In many helicopter accidents, the structural integrity of the air frame is maintained, but the occupants involved often sustain spinal injuries. This is due to the fact that the human body has a relatively low tolerance to forces applied parallel to the spine. Currently, energy absorbing helicopter seat systems utilize load limiting mechanisms to reduce potentially injurious decelerations. Such systems allow limited movement of the seat while the energy is being absorbed. If such devices are designed with "fixed" energy absorber limit loads set only for an occupant of average weight, the system does not perform efficiently at the extremes of the occupant weight spectrum. For example, a heavy occupant may not be restricted sufficiently and may reach the limits of the seat movement, while a lighter occupant will not be able to take advantage of the available stroking distance and will be subjected to higher magnitudes of deceleration than desirable.
To overcme this problem, variable load energy absorbers have been developed wherein the apparatus may be adjusted to accommodate the weight of the occupant. However, such an arrangement has various drawbacks in that the occupant's weight including his suit and other gear with him must be known, in combination with the seat. Care must be taken to make sure that the proper adjustment is made, the accuracy of the apparatus is subject to many variables and the complexity of the system is also disadvantageous.
In one known system, a helicopter seat is slideably mounted to be moveable a short distance downwardly from its normal position in a crash situation. The lower portion of the helicopter shell may be specially constructed to accommodate the downward movement. When the deceleration forces of a crashing helicopter are felt, the chair will move downwardly relative to the air frame so that the occupant does not receive the same forces. Since only a limited space is available for such movement, it is necessary to absorb the energy of the movement. In its known system, energy is utilized to invert a thinwalled, metal tube. Also, rollers are employed to create drag against the exterior of the tube. Variability in the amount of energy absorbed is obtained by controlling the position of the roller relative to the tube. Because of the various shortcomings of such a system as mentioned above, a need exists for a system having improvements over such an arrangement.
In another energy-absorbing or motion-limiting situation, a need exists for a system to protect electronic packages from the shock of explosions in military warfare situations. For example, if a nuclear tactical weapon is detonated, shock waves can destroy unprotected communication systems throughout a very large area. However, by properly protecting such apparatus, very substantial shock waves can be tolerated. Electronic communication packages are often carried in special communication vehicles. Such vehicles are particularly susceptible to such shock waves because of being somewhat more moveable than fixed installations. The system employed to protect the package must, of course, be able to accommodate both the to and the fro movement which occurs with blasts of this nature.
Since the shock can be encountered from any direction, the protection system employed must be able to accommodate such multi-directional forces, which introduces a considerable complexity. It has been suggested that the package to be protected could be mounted or suspended by a group of springs, on all sides of a package. It has been determined, however, that the springs would have to be quite large to accommodate anticipated forces. For example, it has been determined that certain electronic packages can withstand 40 G-level forces. Springs capable of handling such forces would have to be quite large for a substantial package. Further, such system would still be load-sensitive such that the system would have to be specially designed for each package, or a satisfactory load adjusting system could be devised.
Accordingly, a need exists for better solutions to the energy-absorbing problems.